Seismic resilience of typical steel school building and retrofitting options based on FEMA P-58 under mainshock-aftershock effects

This paper investigates the selection of the appropriate retrofitting option for a steel school building based on the resilience index with FEMA P-58 methodology and considers different scenarios of mainshock-aftershock (MS-AS) effects. A typical high school in Kermanshah, Iran, and its two retrofitting options, including retrofitting with concentric braces and retrofitting with shear walls, have been selected as a case study, and their resilience indexes have been evaluated at two hazard levels of 2 % and 10 % in 50 years. In order to calculate the resilience index, seismic damage, repair cost, and repair time of existing school and retrofitting options are evaluated by FEMA P-58 methodology through PACT software. In this study, the effect of the damage level of the mainshock on the total damage of the MS-AS sequences is considered, and the different levels of damage caused by the mainshock are expressed in terms of the maximum inter-story drift ratio (IDR). So in this research, to indicate the mainshock damage on the structure, the response levels of 0.007, 0.025, and 0.05 IDR values have been considered. Investigation of the MS-AS effects on the seismic resilience index of schools shows that the increase in mainshock damage, which is associated with an increase in repair cost and repair time, leads to a reduction in the resilience index of the structures. In this study, the resilience index of the existing school at hazard level 1 has increased from 0.6206 to 0.6916 for the retrofitting with concentric braces and to 0.9620 for shear walls, respectively. Also, at hazard level 2, the resilience index of the existing school has increased from zero to 0.5604 and 0.9287 in retrofitting options with concentric braces and shear walls, respectively. This increase in the resilience indexes shows the positive effect of retrofitting on the seismic performance of the schools. In addition, it was determined that the retrofitting option with shear walls has less repair time and repair cost compared to another option in both hazard levels, so it is finally selected as the appropriate retrofitting option.